The Doctor needs to return to Gallifrey but, because of Romana's action in the previous adventure, he is dreading the paperwork and official inquiry. Instead he convinces Adric they should stop by Earth to take some measurements of a police box before heading to Logopolis to have repairs completed to the Chameleon Circuit. Arriving on Earth the Doctor senses something wrong. A time bubble has formed, causing a TARDIS to appear within a TARDIS. The Doctor fears it's an infinite regression. If so, he and Adric will be trapped forever. Meanwhile Tegan, an Australian airline hostess, enters the Doctor's TARDIS after her car breaks down. Written by
Did You Know?
Christopher H. Bidmead
, a keen computer enthusiast, used many ideas from computer science in developing the story, with elements such as the Monitor, block transfers, and registers all being derived from terminology in computer architecture. Eager to inject Doctor Who with real scientific notions, Bidmead also drew upon the physics discipline of thermodynamics, making heavy use of the concept of entropy: the measure of unavailable energy in a system, which effectively increases as a system becomes homogeneous. Another starting point was Nathan-Turner's observation that a real police box still stood on the Barnet bypass in London. Bidmead was fascinated with the TARDIS, and wanted to explore its properties more fully. See more
[looking into Romana's room
Ha. I suppose I'm gonna miss Romana.
And K-9, too.
[turning swiftly away
Yes. Still, the future lies this way.
Featured in A New Body at Last